gentamicin, kanamycin and amikacin drugs as non -toxic ...aluminum (al) and its alloys represented...
TRANSCRIPT
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Int. J. Electrochem. Sci., 10 (2015) 9808 - 9823
International Journal of
ELECTROCHEMICAL SCIENCE
www.electrochemsci.org
Gentamicin, Kanamycin and Amikacin Drugs as Non -Toxic
Inhibitors for Corrosion of Aluminum in 1.0M Hydrochloric
Acid
M. Abdallah1,2,*
, B.A.AL Jahdaly1
1Chemistry Department, Faculty of Applied Sciences, Umm Al-Qura University, Makkah, Saudi
Arabia. 2Chemistry Department, Faculty of Science, Benha University, Benha, Egypt
*E-mail: [email protected]
Received: 16 September 2015 / Accepted: 14 October 2015 / Published: 4 November 2015
The inhibition effect of three molecules of antibiotic drugs, namely, gentamicin, kanamycin, amikacin
on aluminum corrosion in 1.0 M HCl solution has been investigated using weight loss, hydrogen
evolution reaction, galvanostatic polarization and electrochemical impedance spectroscopy techniques.
The inhibition efficiency increases with increasing the concentration of inhibitor and decreasing
temperature. Polarization measurements showed that the studied antibiotic compounds acting as mixed
type inhibitors. The adsorption follows the Langmuir isotherm model. Some activated thermodynamic
parameters are calculated and explained. One capacitive loop was observed for all spectra in EIS
indicating that the corrosion of aluminum corrosion is under charge transfer control.
Keywords: Antibiotic drugs, Aluminum, Corrosion inhibitors, Adsorption, EIS.
1. INTRODUCTION
Aluminum (Al) and its alloys represented as an important class of materials due their high
technological value and their wide range of industrial applications, particularly in aerospace, motor
vehicle, home industries, pipes, chemical batteries and other studies [1,2]. Acidic solutions are mainly
used for chemical and pickling and electrochemical etching of aluminium. It is greatly important to use
corrosion inhibitors to decrease the corrosion rate of aluminum in HCl solutions. In most cases, the
corrosion inhibitors are mainly organic compounds containing hetero atoms, aromatic rings or multiple
bonds [3-18]. It has been known that the first step in the mechanism of inhibition of Al in aggressive
HCl solution is generally the adsorption of the organic compounds onto the metal surface. The strength
of adsorption process mainly depends on the chemical structure of the adsorbed compound and its
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Int. J. Electrochem. Sci., Vol. 10, 2015
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properties such as functional groups, aromaticity and the electron density of the donor atoms-orbital's
characters of donating electrons [19]. Thus, development of novel non-toxic corrosion inhibitors have
a greet considerable due to their environmental importance [20,21]. In recent years, more attention has
been paid from researchers to develop some kinds of drug compounds to be used as corrosion
inhibitors for different metals [22-26]. In the previous studies antihypertensive and antibacterial drug
compounds were employed as corrosion inhibitors for aluminium in acid media [27,28].
Our work aims to study the effect of three molecules of antibiotic drugs, namely, gentamicin,
kanamycin, amikacin toward the aluminum corrosion in 1.0 M HCl solution using weight loss,
hydrogen evolution, galvanostatic polarization and EIS methods. The percentage inhibition efficiency
was calculated using the above techniques. The effect of rising temperature on the dissolution of Al in
1.0 M HCl solution containing 1000 ppm of antibiotic drugs was studied and some thermodynamic
parameters of activation were calculated and discussed.
2. EXPERIMENTAL METHODS
Aluminum with high purity 99. 99% provided by "Aluminum Company of Egypt, Nagh
Ammady" was used as working electrode. For weight loss measurements and the hydrogen evolution
reaction, the test Al coupons having dimension 2.0x 1.0 x 0.2 cm3
were abraded with a series of emery
papers (grades 320, 600, 800 and 1200) and then washed with bi distilled water and acetone. Finally,
dried between two filter papers. The procedure methods of weight loss and hydrogen evolution
reaction measurements were carried out as described elsewhere [15,29].
Table 1. The chemical structure of antibiotic drugs
Compounds
Structure
Compound I
Gentamicin
O
O
HO NH2
OO
HN
NH
OH
HO
NH2
H2N
Molecular Formula: C21H43N5O7
Molecular Weight: 477.59542 g/mol
2-((4,6-diamino-3-((3-amino-6-(1-(methylamino)ethyl)tetrahydro-2H-
pyran-2-yl)oxy)-2-hydroxycyclohexyl)oxy)-5-methyl-4-
(methylamino)tetrahydro-2H-pyran-3,5-diol
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CompoundII
Kanamycin
O OH
OH
OH
NH2
O
OH
NH2
H2N
O
O
H2N OH
HO
HO
H2SO4
Molecular Formula: C18H36N4O11
Molecular Weight: 484.49864 g/mol
2-(aminomethyl)-6-((4,6-diamino-3-((4-amino-3,5-dihydroxy-6-
(hydroxymethyl)tetrahydro-2H-pyran-2-yl)oxy)-2-
hydroxycyclohexyl)oxy)tetrahydro-2H-pyran-3,4,5-triol hydrosulphuric
Compound III
Amikacin
HO
O
OH
O
NH2
OH
OH
O
O
HNO
OH
H2NH2N OH
OH
OH
H2N
Molecular Formula: C22H43N5O13
Molecular Weight: 585.60252 g/mol
4-amino-N-(5-amino-2-((4-amino-3,5-dihydroxy-6-
(hydroxymethyl)tetrahydro-2H-pyran-2-yl)oxy)-4-((6-(aminomethyl)-
3,4,5-trihydroxytetrahydro-2H-pyran-2-yl)oxy)-3-hydroxycyclohexyl)-
2-hydroxybutanamide
Electrochemical measurements were carried out using Aluminium specimen in the form of a
rod of 0.48 cm2 exposed surface area as a working electrode. The polishing, degreasing and washing of
the Al electrode as explained in the above techniques. A PS remote potentiostat with PS6 software to
calculate the corrosion parameters was used for the galvanostatic polarization measurements. EIS
measurements were performed at a frequency range from 10 kHz to 100 mHz and signal amplitude
perturbation of 5 mV by using a computer- controlled potentiostate (Auto Lab 30, Metrohm). All the
above experiments were performed at 30±1oC by using ultra circulating thermostat.
The chemical structure of antibacterial drugs is shown in Table 1
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3. RESULTS AND DISCUSSION
3.1. Weight loss measurements
Figure 1 represents the weight loss- time relationship for the Al corrosion in 1.0 M HCl
solution in the presence and absence of various concentrations of compound (III) at 30±1oC, as a
representative example of the studied compounds. Similar curves were obtained for compounds I and
II (not shown). The weight loss of Al is decreased. This means that antibiotic molecules slow down the
rate of corrosion of Al in 1.0 M HCl solution or in other words, these molecules act as inhibitors.
Figure 1. Weight loss-time curves for aluminum dissolved in 1.0 M HCl in the absence and presence
of various concentrations of compound III at 30OC. 1- 0.00ppm compound III, 2- 200ppm,
3-400ppm, 4-600ppm, 5-800ppm, 6-1000ppm
As shown by Fig. 1, there is a linear variation of weight loss with time in the absence and
presence of inhibitors indicating the absence of insoluble film formation on aluminum surface during
corrosion. The investigated compounds are adsorbed first onto the Aluminum surface and thereafter
suppress corrosion action either by blocking the reactive sites or by modifying both the cathodic and
anodic partial process mechanisms.
The corrosion rate was calculated according to the following relation [30],
Rcorr = W/St (1)
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where, W(mg) is the weight loss, S is the surface area and t is the immersion time. The
surface coverage (θ) and the percentage inhibition efficiency (% IE) were calculated using the
following relations:
=
free
add
R
R1 (2)
% I.E = 1001
free
add
R
R (3)
where, Rfree and Radd are the weight loss of Al coupons in the absence and presence of
inhibitors, respectively.
The values of Rcorr., % IE and θ at 30oC are given in Table 2. The values of Rcorr decrease
and the values of % IE increase, indicating the inhibiting effect of the investigated drug molecules and
decreases in the following order:
Compound III > Compound II> Compound I
This order will be discussed later.
3.2. Effect of temperature
The effect of increasing temperature on the weight loss of aluminum in 1M HCl solution in the
absence and presence of 1000ppm of antibiotic drugs was investigated by weight loss measurements in
temperature ranges from (30 to 60oC). Similar curves in Fig. 1 were obtained (not shown). As the
temperature rises, the weight loss and the corrosion rate increases and hence the inhibition efficiency,
decrease and this is due to the desorption is more easier by increasing the temperature, which
indicating that the adsorption of antibiotic drugs on the Al surface occurs through physical adsorption
The activation energy Ea for the corrosion of Al electrode in the absence and presence of 1000
ppm of the antibiotic drugs was calculated using Arrhenius type equation [31,32],
Log Rcorr= log A – (Ea/2.303RT) (4)
Where, Ea is the apparent activation energy, R is the universal gas constant, A is the Arrhenius
pre-exponential factor, T is the absolute temperature
Fig. 2 represents a linear relationship between (log Rcorr), with (1/T) for Al in 1.0M HCl
devoid of and containing 1000 ppm of the antibiotic drugs with slope equal to -Ea*/ 2.303R. The
calculated values of Ea obtained from the slope of the straight line are equal to 17.45.18KJ mol-1
in
1M HCl and equal 23.78, 24.62 and 25.18 KJ mol-1
for compounds I, II and III, respectively.The
increase in the activation energy in the presence of antibiotic drugs, indicating the adsorption of the
inhibitor molecules on the Al surface making a barrier for mass and charge transfer. The enthalpy and
entropy of activation for the corrosion of Al in the absence and presence of drug molecules were
calculated using the transition state equation [31,32],
log (Rcorr / T) = [(log R/hN) +( ΔS*/2.303RT)] - ( ΔH
* /2.303RT) (5)
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where, h is Planck’s constant, N is Avogadro's number, ΔS*is the entropy of activation and
ΔH* is the enthalpy of activation.
Table 2. Effect of antibiotic drug concentrations on the rate of corrosion (Rcorr.), inhibition efficiency
(%I.E) and surface coverage (θ) obtained from weight loss and hydrogen evolution
measurements for corrosion of Al in 1.0M HCl solution.
Concentrations
Rcorr. mg.cm
-2.min.
-1
%IE
fromWeight
Loss
θ %IE from H2
Evolution
1 M HCl + compound I
00.0ppm compound I 0.443 - - -
200ppm compound I 0.096 78.33 0.783 77.45
400 ppm compound I 0.085 80.81 0.808 81.73
600 ppm compound I 0.073 83.52 0.835 83.96
800 ppm compound I 0.061 86.23 0.862 86.89
1000 ppm compound I 0.048 89.16 0.892 90.06
1 M HCl + compound II
200 ppm compound II 0.087 80.36 0.804 81.10
400 ppm compound II 0.072 83.74 0.837 83.98
600 ppm compound II 0.056 87.53 0.875 88.12
800 ppm compound II 0.045 89.84 0.899 90.41
1000 ppm compound II 0.039 91.19 0.912 91.86
1 M HCl + compound III
200 ppm compound III 0.067 84.87 0.849 85.04
400 ppm compound III 0.053 87.75 0.877 88.01
600 ppm compound III .0.044 90.06 0.901 90.56
800 ppm compound III 0.036 91.87 0.919 92.41
1000 ppm compound III 0.028 93.68 0.937 93.12
Fig. 3 represents the relation between of (log Rcorr /T), with (1/T) for Al in 1.0 M HCl
containing 1000 ppm of the studied compounds. Straight lines were obtained with a slope of (-
H*/2.303 R) and an intercept [log (R/Nh -So /2.303R)]. The values of H* obtained from the slope
of the straight line equal to 22.18KJ mol-1
in 1M HCl and equal to 25.16, 26.48 and 26.99KJ mol-1
in
the presence of compounds I, II and III, respectively. These values indicate that, the increase in the
enthalpy of activation (H*) in the presence of the inhibitors implies that the addition of the inhibitors
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Int. J. Electrochem. Sci., Vol. 10, 2015
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to the acid solution increases the barrier energy limit of the corrosion reaction to a level depends on the
type and concentration of the present inhibitor. The positive values of H* reflect that the adsorption
process of the investigated inhibitors on the aluminum surface is an endothermic process
Figure 2. Relation between log Rcorr and the reciprocal of temperature of Al electrode in a) 1.0 M HCl
b) 1.0 M HCl + 1000 ppm of the studied compounds 1)compound I 2) compound II
3)compound III
Figure 3. Relation between log Rcorr/T and the reciprocal of temperature of Al electrode in a) 1.0 M
HCl b) 1.0 M HCl + 1000 ppm of the studied compounds 1)compound I 2) compound II
3)compound III
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The values of S* obtained from the intercept of a straight line equal to - 212.34 J mol
-1 k
-1 in
1.0MHCl solutions and -243.75 ,254.68 and 258.71 J mol-1
k-1
in the presence of compounds I, II and
III, respectively.
The negative values of S* indicates that the activation complex formation is the rate
determining step represents an association rather than dissociation [33].
3.3. Hydrogen evolution measurement
Fig. 4 shows the relation between the volume of hydrogen evolved with time for the dissolution
of Al in 1.0 M HCl solution in the absence and presence of various concentrations of compound III as
an example of the tested inhibitors.. Similar curves were obtained for other two compounds I and II
(not shown). It is clear that from Fig 4. The rate of hydrogen evolution at the beginning of the reaction
is low due to the stability of the aluminium oxide (Al2O3) film formed at the surface of Al. After
certain times the rate of H2 evolved increases due to start of the dissolution of Al to Al+3
. This time is
called induction time.
Figure 4. Relation between the volume of hydrogen evolved and time for the corrosion of aluminum
in 1 M HCl in devoid of and containing various concentrations of compound III at 30oC. 1-
0.00ppm compound III, 2- 200ppm, 3-400ppm, 4-600ppm, 5-800ppm, 6-1000ppm
The corrosion rate was obtained from the slope of the straight portion of curves after induction
time. As the concentration of antibiotic drugs increases the rate of H2 evolved decrease and the
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induction time increases, hence the rate of corrosion decreases and the inhibition efficiency increases.
This indicates that the inhibiting effect of antibiotic compounds
The percentage inhibition efficiency (% IE) was calculated using the following equations:
% IE = [1- R free / Radd] 100 (6)
where, Rfree and Radd are the corrosion rate of Al coupons in the absence and presence of
inhibitors, respectively
The calculated values of (% IE) are given in Table 1. and have the following order:
Compound III > Compound II> Compound I
3.4. Galvanostatic polarization
Fig.5. shows the cathodic and anodic polarization curves of Aluminium electrode in 1.0 M
HCl solution in the absence and presence of various concentrations of compound III as a
representative example of antibiotic molecules. Similar curves were obtained for compounds I, II (not
shown).
Figure 5. Cathodic and anodic polarization curves of Al electrode in 1.0 M HCl solution in the
absence and presence various concentrations of compound III. (1) 0.00ppm compound III,
(2) 200ppm, (3) 400ppm, (4) 600ppm, (5) 800ppm, (6) 1000ppm
The corrosion parameters such as, anodic Tafel slope (a), cathodic Tafel slope (C), corrosion
potential (Ecorr.), corrosion current density (Icorr), and inhibition efficiency (% IE.) were calculated and
given in Table 3.
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The percentage inhibition efficiency (%IE) was calculated from corrosion current density
values using the equation.
% IE =
free
add
I
I1 100 (7)
where, Ifree and Iadd are the corrosion current densities in the absence and presence of
inhibitors.As the concentration of antibiotic molecules increases The values of anodic (ba) and cathodic
(bc)Tafel slopes are nearly constant indicating that these compounds are of mixed type inhibitors. i.e.,
reduce the anodic and retard the cathodic hydrogen evolution reaction. The values of Ecorr are shifted to
slightly negative potentials and the values of Icorr. decreases. Hence the values of %IE increases,
indicating the inhibiting effect of the investigated compounds. The calculated values of the percentage
inhibition efficiency of antibiotic molecules.decrease in the following order: Compound III >
compound II > compound I
Table 3. Corrosion parameters of Al electrode in 1.0 MHCl solution containing various
concentrations of of antibiotic drugs.
Inhibitor Conc.,
ppm
bc
mV dec-1
ba
mVdec-1
-Ecorr. mV(SCE)
Icorr.
μA cm-2
%IE
Compound I
0 346 636 748 1258 - 200 345 637 750 281 77.66
400 341 638 752 233 81.47
600 345 635 753 208 83.46
800 344 638 756 162 87.12
1000 344 637 755 112 91.09
Compound II
0 346 636 748 1258 - 200 344 634 746 242 80.76
400 342 636 748 195 84.49
600 348 635 749 152 87.92
800 347 836 750 118 90.62
1000 346 633 751 96 92.36
Compound III
0 346 636 748 1258 - 200 345 631 749 199 84.18
400 344 630 750 145 88.47
600 342 632 750 110 91.25
800 344 633 752 92 92.68
1000 345 637 753 80 93.64
3.5. Electrochemical impedance spectroscopy (EIS)
Figs. 6 show the Nyquist plots for aluminum electrode in 1.0 M HCl solution in the absence
and presence of various concentrations of compound III as a representative example of antibiotic
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molecules. Similar curves were obtained for compounds I and II (not shown). The semicircular
appearance being observed both in the absence and presence of various concentrations of antibiotic
molecules indicating that the corrosion of Al in 1.0 M HCl is mainly controlled by the charge transfer
process [34]. The diameter of the capacitive loop increase with increasing the concentration of
inhibitors indicating the strengthening of inhibiting film. The impedance spectra of the Nyquist plots
(Fig.6) were analyzed by fitting the experimental data to a simple equivalent circuit model which
shown in Fig. 7, which includes the solution resistance Rs and the double layer capacitance Cdl which
is placed in parallel to the charge transfer resistance Rct [35,36].
0 200 400 600 800 1000 1200 1400 1600
0
100
200
300
400
500
600
- Z
i (o
hm
cm
-2)
Zr (ohm cm
-2)
1
2
3
4
5
6
Figure 6. The Nyquist plots for aluminum in 1.0M HCl solution in the absence and presence of
various concentrations of compound III at 300C 1- 0.00ppm compound III, 2- 200ppm, 3-
400ppm, 4-600ppm, 5-800ppm, 6-1000ppm
Figure 7. The equivalent circuit model used to fit the experimental results.
Rct
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The various parameters obtained from the analysis of Nyquist plots are the resistance of charge
transfer Rct (diameter of the high frequency loop) and the capacity of double layer Cdl which is defined
as:
ctmax
dlR f 2
1C
(8)
Where Rct is the charge transfer resistance in the presence of inhibitor and fmax is maximum
frequency.
The inhibition efficiency obtained from the impedance measurements is calculated by the
following relations:
% 1 100ct
ct
RIE x
R
(9)
Where, Roct and Rct are the charge transfer resistance in the absence and presence of inhibitor,
respectively. The associated with the diagrams impedance are given in Table 4.
An inspection of Table 4, as the concentration of antibiotic molecules increases, the values of
Rct increases and hence the percentage inhibition efficiency increases due to the formation of adherent
film on the Al /solution interface. The values of Cdl decrease due to the gradual replacement of water
molecule by the adsorption of the antibiotic compounds which form a protective film on the Al surface
and led to the decrease in local dielectric constant of the metal solution interface.
The percentage inhibition efficiency obtained from EIS measurements decreases as follows:
compound (III) > compound (II) > compound (I)
Table 4. in 1.0 M HCl solution in the absence and presence of various concentrations of antibiotic
molecules at 25 ºC. Electrochemical impedance parameters obtained from the Al electrode
Inhibitor
Conc.
(ppm)
Rs
(Ω cm²)
Rct
(Ω cm²)
Cdl
(µF cm-2
) %I.E
Free 1.0M HCl 8.60 98 25.30 -
Compound I
200 9.86 418 23.75 76.55
400 10.03 498 21.87 80.32
600 11.42 715 19.64 86.29
800 12.86 755 17.84 87.02
1000 13.98 998 15.66 90.18
Compound II
200 10.68 506 23.06 80.63
400 12.64 576 18.82 82.98
600 14.06 695 16.88 85.89
800 15.68 982 16.22 90.00
1000 17.86 1085 14.47 90.96
Compound III
200 11.55 598 22.50 83.61
400 13.80 753 19.33 87.03
600 15.44 951 18.47 89.69
800 16.95 1200 15.08 91.83
1000 18.40 1531 11.50 93.59
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The order of inhibition efficiency obtained from the EIS technique were in full accord with
those obtained from the weight loss and hydrogen evolution reaction and galvanostatic technique. This
proves the validity of these tools in the measurements of the investigated inhibitors.
3.6 Inhibition mechanism and adsorption isotherm
From the results of both chemical and electrochemical measurements obtained above for the
corrosion of Al in 1.0 M HCl solution by using some selected antibiotic compounds it was found:
1- The corrosion rate decreases with increasing the concentration of the inhibitor.
2- Weight loss is varied linearly with time.
3- The percentage inhibition efficiency (% IE) decreases with increasing temperature.
4- The rate of hydrogen evolution and the corrosion current density (Icorr) decreases with
increasing the inhibitor concentration.
5- The values of charge resistance transfer decrease while the double layer capacity
increases with increasing the inhibitor concentration.
These results indicate that the inhibition of aluminum corrosion in HCl in the presence of the
investigated drug compounds is due to their adsorption at the electrode-solution interface depending on
their adsorption active centers, charge density and molecular size [37]. It is generally believed that the
adsorption of the antibiotic drugs at the Al / solution interface is the first step in the mechanism of
inhibitory action in HCl solution. The adsorption of drug molecules at the metal /solution interface can
be elucidated by substitution adsorption between drug molecules in the aqueous solution and the
water molecule on the metal surface.
Drug(sol) + xH2O(ads) Drug (ads) + xH2O(sol) (10)
Where, Drug(sol) and Drug (ads) are drug molecules in solution and adsorbed on the metal
surface, respectively. H2O(ads) is water molecule on metal surface, H2O(sol) is water molecule in
solution and x is the size ratio represent the number of water molecules replaced by one dug molecule.
The inhibition of the investigated antibiotic molecules can be attributed to the presence of
heterocyclic rings containing hetero atoms of oxygen and the amino groups (-NH2) in the chemical
structure of the studied compounds which led to the formation of more reaction centers for the
adsorption. Hence, the adsorption effect of drug molecules could be explained on the basis of the
formation of coordination bonds between the unshared electron pairs of oxygen and nitrogen atoms
and the empty p-orbits of aluminum. The order of percentage inhibition efficiency (% IE) decreases as
follows: compound (III) > compound (II) > compound (I). This is consistent with the molecular
weight and the number of hetero atoms (oxygen and nitrogen) within these compounds.
Attempts were made to fit the surface coverage () to various isotherm including Langmuir,
Freundlich, Frumkin, Temkin and Flory-Huggins. By far the best results are obtained with Freundlich
adsorption isotherm and can be represented using the following equation [38],
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Int. J. Electrochem. Sci., Vol. 10, 2015
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θ = KCn (11)
or alternatively by:
log θ = log K + n log C (12)
where, K and C are the equilibrium constant of the adsorption process and additive
concentration, respectively.
Figure 8. Freundlich adsorption isotherm for Al in 1.0 M HCl solution in the absence and presence of
antibiotic drug compounds 1)compound I 2) compound II 3)compound III
Fig 8 represents the plot of log θ versus log C.A straight lines were obtained with intercept of
log K.
The equilibrium constant of adsorption, K, is related to the standard free energy of adsorption,
∆Goads, according the following equation [23],
K=1/55.5 exp (- ∆Goads /RT) (13)
Where, T is the absolute temperature and R is the gas constant (8.314 J. mol-1
.K-1
). The
numerical value 55.5 is the concentration of water in mol.L-1
The values of K are equal to 0.758, 0.776 and 0.822 for compounds I, II and III, respectively.
The high value of K indicates that the strong adsorption of antibiotic drugs on the Al surface. The
calculated values of Go
ads for antibiotic drug compounds on the Al surface are equal to –34.56, –
36.48 and –38.62kJ mol–1
for compounds I, II, and III, respectively.
The free energy change of adsorption is associated with water adsorption/desorption
equilibrium which forms an important part in the overall free changes of adsorption. The negative
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Int. J. Electrochem. Sci., Vol. 10, 2015
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values of [31,32], Goads obtained indicates that the adsorption process of antibiotic drugs on the Al
surface is spontaneous one.
4. CONCLUSIONS
1-Antibiotic drugs are good inhibitors for the corrosion of aluminum in 1.0 M HCl solution.
2-The inhibition efficiency increases with increasing the concentration of antibiotic drugs and
with decreasing temperature.
3-The inhibition process is due to the horizontal adsorption of antibiotic drugs on the Al
surface.
4-The adsorption obeys Langmuir isotherm.
5-Antibiotic drugs act as mixed –type inhibitors.
6-EIS measurements indicate that the corrosion reaction is controlled by charge transfer
process
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